Prepare the Vegetables: Slice the aubergines into 1/4-inch thick rounds. Optionally, peel and slice the potatoes into similar-sized rounds. Sprinkle the aubergine slices with salt and let them sit for 20-30 minutes to remove excess moisture and bitterness. Rinse and pat them dry with a paper towel. Heat olive oil in a frying pan and lightly fry the aubergines and potatoes until golden. Place them on a paper towel to drain excess oil.

Make the Meat Sauce: Heat olive oil in a large skillet over medium heat. Add the chopped onion and garlic, cooking until softened. Add the ground meat, breaking it apart with a wooden spoon. Cook until browned. Stir in the tomato paste, crushed tomatoes, and red wine (if using). Season with cinnamon, oregano, nutmeg, salt, and pepper. Simmer the sauce for 15-20 minutes until thickened and aromatic.

Prepare the Béchamel Sauce: Melt the butter in a saucepan over medium heat. Add the flour and whisk constantly to form a smooth paste (roux). Gradually pour in the warm milk, whisking to avoid lumps. Cook until the sauce thickens. Remove from heat and stir in the Parmesan cheese, nutmeg, and seasoning. If desired, whisk in an egg yolk for extra richness.

Assemble the Musakka: Preheat your oven to 180°C (350°F). In a baking dish, layer the ingredients as follows: a layer of fried potatoes (optional), a layer of fried aubergines, spread the meat sauce evenly over the vegetables, repeat with another layer of aubergines and meat sauce if desired. Pour the béchamel sauce over the top, spreading it evenly to cover the dish. Sprinkle with a little extra Parmesan for a golden crust.

Bake the Musakka: Place the dish in the preheated oven and bake for 40-50 minutes, or until the top is golden and bubbly. Let the musakka cool for 10-15 minutes before slicing and serving.